Membrane valves are used in a variety of fields and more particularly in underwater breathing apparatus, for example to regulate air outflow in pressure regulators and water outflow in masks and snorkels.
FIG. 1 illustrates a membrane valve according to the prior art, which comprises a shutter disk 1 of flexible material and a valve seat 2 with a continuous surface and one opening. Shutter disk 1 includes a cap of circular perimeter with a central portion that is essentially flat and further with a peripheral sealing lip 101, of essentially conical shape, that rests on annular wall 202 of valve seat 2. A primary clamping pin 201 extends from the central portion of the concave side of the cap of shutter disk 1 and elastically engages shutter disk 1 in the opening of valve seat 2.
The side of valve seat 2 that is opposite to shutter disk 1 delimits a chamber with controlled pressure. As shown in FIG. 2, in the event of overpressure within the chamber, shutter disk 1 deforms from its rest position and sealing lip 101 lifts up from annular wall 202, causing the membrane valve to open. While the lifting height of sealing lip 101 is substantially uniform along the perimeter of shutter disk 1, the outflow of gas or liquid through the central opening of valve seat 2 causes a swelling deformation of shutter disk 1. Because some of the chamber overpressure is absorbed by the deformation of shutter disk 1, such swelling deformation contributes beneficially to a decrease in chamber pressure, but at the same time hinders the outflow of liquid or gas through the valve opening, causing only a relatively thin passage to develop between sealing lip 101 and circular wall 202.
FIG. 3 illustrates a variation in the prior art wherein a shutter disk of elongated shape is employed. In this variation, the shutter disk may have one primary clamping pin, as shown in FIG. 3, or two primary clamping pins, each situated substantially in one of the foci of the elongated shape or in one of the centers of the arched end. While the elongated shape increases the outflow area due to the longer perimeter of sealing lip 101, the two-pin design does not improve on the swelling problem encountered with circular membranes and with one-pin designs. On the contrary, the portion of the shutter disk situated between the two primary clamping pins is more prone to swelling than with a single pin design, thereby causing the detrimental effect on the outflow of liquid or gas to worsen as compared to a one-pin design.
The swelling problems of shutter disks are also present in membrane valve designs wherein no annular wall 202 is present on the surface of valve seat 2.
Membrane valves are employed in a variety of applications. Specifically, membrane valves are employed in second stage pressure reducers for two-stage underwater regulators to regulate the outflow of spent gas that the diver has exhaled.
In second stage pressure reducers according to the prior art, a case contains a supply chamber where breathing gas is stored. Breathing gas is drawn into the supply chamber through an inlet connected to a first stage pressure reducer, which inlet is opened or closed by a spring valve housed inside the supply chamber. The spring valve opens when a depression, generally caused by the inhalation of the diver, causes the spring to contract and remains closed otherwise. Breathing gas is eventually delivered to the user through a mouthpiece connected to an outlet extending from the supply chamber.
A level area on the peripheral wall of second stage case includes a membrane valve regulating the outflow of spent gas that the user has exhaled. The membrane valve comprises a valve seat with an annular wall, which annular wall is in sealing contact with the sealing peripheral lip of the shutter disk, and the valve seat further comprises an opening, through which the spent gas is discharged. A primary clamping pin engages the shutter disk to the valve seat.
The shutter disk is in contact with the outer face of the level area on the second stage case and may be surrounded by an outflow duct, which is defined by the peripheral wall of the second stage case and by a C-shaped element affixed to the second stage wall. The outflow duct communicates with the external environment through orifices at the head sections of such outflow duct.